Stretch-activated elastic composite

ABSTRACT

A stretch-activated elastic composite includes a non-woven fabric having a potential elongatability of higher than 100% in a predetermined direction, and an elastically recoverable, elastic sheet. The elastic sheet in its unstretched state is partially bonded to the non-woven fabric in its unelongated state. The elastic composite exhibits, per unit width of 5 cm, (1) a stress of lower than 1000 g at 30% stretch, (2) a stress of higher than 400 g at 100% stretch, (3) a breaking point of higher than 400 g and (4) an elastic limit of higher than 200%. The elastic composite after being stretched at a rate of lower than 200% exhibits, per unit width of 5 cm, (1) a stress of lower than 500 g at 30% stretch and (2) a stress of higher than 100 g at 100% stretch. The elastic composite after three repeated cycles of 150% stretching and relaxing exhibits an elastic recovery rate of higher than 60%. The elastic composite of the present invention provides excellent performance in elastic recovery, is soft to the touch, and is best utilized in elasticizing an article portion which is brought into direct contact with human skin.

FIELD OF THE INVENTION

The present invention relates to an elastic composite which comprises anon-woven fabric and an elastic sheet, and which exhibits excellentelastic recovery and a soft surface touch. The elastic composite can beadvantageously utilized in elasticizing an article which is brought intodirect contact with the human skin during use, such as a sleeve of amedical gown, or a waist or crotch portion of a sanitary article.

BACKGROUND OF THE INVENTION

In recent years, disposable articles, including medical and sanitaryarticles, etc., have widely used elastic material to improve the fit tothe human body. Particularly, infant articles utilize an elastic sheetand a non-woven fabric composite much more frequently than an elasticsheet alone. In the elastic sheet and the non-woven fabric composite,the elastic sheet exhibits elastic properties and the non-woven fabricprovides improved surface structure and reinforcement of the elasticsheet.

A typical example of such an elastic composite is a three-layercomposite called S.M.S. (spunbonded/meltblown/spunbonded) which isdisclosed in U.S. Pat. Nos. 4,663,220; 4,652,487; and 4,720,415. Thiscomposite is manufactured by a method called S.B.L. (Stretch-BondedLaminate) wherein the elastic sheet is first stretched and is in itsstretched state bonded to the non-woven fabric to form the compositeupon release. The composite manufactured in accordance with this methodhas a stable range of elasticity and neither expands beyond the rangenor breaks during normal use since its expansion limit corresponds toits stretched range during manufacture. However, the compositedisadvantageously uses more of the non-woven fabric than may benecessary and is bulky so that it is not well-suited for high-speedcommercial production.

Japanese Patent No. 4-281059 also discloses a method for directlyentangling fibers into an elastic net, which, however, is costly. Inorder to remedy these drawbacks, an attempt (EPC No. 556,749) has beenmade to bond an elongatable non-woven fabric to an elastic film on lineto form a composite of channel-like construction.

Japanese Utility Model No. 3-39509 discloses an elastic composite whichis constructed by hydro-entangling a web comprising staple fibers and anon-woven fabric directly formed of thermoplastic elastomers. In orderfor the composite to have stretchability of higher than 70%, the webincludes fibers which slightly crimp upon application of heat or whichsplit into fibers of finer than 1 denier.

The above conventional composites are capable of expanding over a widerange from a breaking point of the non-woven fabric to a breaking pointof the elastic sheet. Their critical points however create difficulty indesigning products and defining its specifications. It also leaves userswith insufficient knowledge of the proper use since they do not know atwhat point the composite breaks.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a highly productive,economical and functional elastic composite which utilizes individualproperties of a non-woven fabric and an elastic sheet in combination.Another object of the invention is to provide a method for manufacturingsuch an elastic composite.

In accordance with the embodiments of the present invention, there isprovided a stretch-activated elastic composite which comprises anon-woven fabric having a potential elongatability of higher than 100%in a biased direction, an elastic sheet having an elastic recovery rateof higher than 60%, and an elastic limit of higher than 200%. Thenon-woven fabric in its unelongated state is partially bonded to onesurface of the unstretched elastic sheet in securement regions. Theelastic composite exhibits, per unit width of 5 cm, (1) a stress oflower than 1000 g at 30% stretch, (2) a stress of higher than 400 g at100% stretch, (3) a breaking point of higher than 400 g, and (4) anelastic limit of higher than 200%. The elastic composite after beingstretched less than 200% exhibits, per unit width of 5 cm, (1) a stressof lower than 500 g at 30% stretch and (2) a stress of higher than 100 gat 100% stretch. The elastic composite after three repeated cycles of150% stretching and relaxing exhibits an elastic recovery rate of higherthan 60%. “Strain” as used herein means the amount of elongation of thematerial when a stretching force is applied. “Stress” is the forceapplied to produce the strain.

In order to optimize the elastic composite structure in accordance withthe preferred embodiments of the present invention, it becomes importantto combine respective characteristics of the non-woven fabric and theelastic sheet thereby improving their functions synergistically. Sincethe elastic sheet may be expensive relative to the non-woven fabric, theaddition of the non-woven fabric thereto further improves thecost/performance ratio of the elastic composite.

In accordance with the present invention, the designs of the expandablenon-woven fabric and selections of the bonding method provide a widerange of selection of the elastic sheet and permit the elastic sheet tofully exhibit its desired functionality.

(1) The expandability of the non-woven fabric enables the elasticcomposite, which is not elastically stretchable in a normal condition,to have the property that it is activated by expansion to becomeelastically stretchable and contractable.

(2) With a suitable selection of its entanglement condition anexpandable, hydro-entangled non-woven fabric enables the resultingnon-woven fabric to have good expandability as well as two-phaseexpandability which creates a second increase in stress beyond a firststress point.

(3) Securement regions for securing the elastic sheet to the non-wovenfabric are provided to extend transversely of the expandable directionof the elastic composite so that the securement regions provide lessresistance to the expandability of the elastic composite.

(4) The securement regions provided between the non-woven fabric and atop surface of the elastic sheet are staggered from the securementregions provided between the non-woven fabric and a bottom surface ofthe elastic sheet to prevent the top and bottom securement regions fromoverlapping. This prevents brittleness. Where heat bonding is used, somebrittleness may occur where the heat is applied. By staggering, asdescribed, such brittleness (which may be undesirable) does not extendthrough the composite.

The above considerations in designing the elastic composite enableproduction of an elastically recoverable elastic composite which hasexcellent expandability under low strain.

The present invention further provides a method for manufacturing anelastic composite having the above-described characteristics. Thismethod will now be explained in detail with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a graph showing S-S (stress-strain) curves of an elasticcomposite in accordance with the present invention.

FIG. 2 is a graph showing S-S curves of another elastic composite inaccordance with the present invention.

FIG. 3 is a graph showing S-S curves of the elastic composite whenstretched at a selected rate and released.

FIG. 4 is a graph showing S-S curves of the elastic composite whenstretched at a rate different from that of FIG. 3 and released.

FIG. 5 is a graph showing S-S curves of the elastic composite whenstretched at a rate different from that of FIG. 3 and released.

FIG. 6 is a graph showing S-S curves of the elastic composite whenstretched at a rate different from that of FIG. 3 and released.

FIG. 7 is a graph showing S-S curves of the elastic composite whenstretched at a rate different from that of FIG. 3 and released.

FIG. 8 is a graph showing S-S curves of three different non-wovenfabrics hydro-entangled by regular means when they are stretched both inthe MD (machine direction) and in the CD (cross direction).

FIG. 9 is a graph showing S-S curves of the non-woven fabric used in thepresent invention when stretched both in the MD and in the CD.

FIGS. 10A, 10B and 10C are schematic cross-sectional views respectivelyillustrating exemplary arrangements of the elastic sheet and thenon-woven fabric in accordance with the present invention.

FIGS. 11A, 11B and 11C are representative plan views illustratingexemplary patterned provisions of intermittent securement regions in theelastic composite of the present invention.

FIGS. 12A, 12B and 12C are representative plan views illustratingexemplary arrangements of intermittent securement regions in the elasticcomposite of the present invention.

FIG. 13 is a plan view illustrating an exemplary arrangement ofintermittent securement regions in the elastic composite of the presentinvention.

FIG. 14 is a plan view illustrating another exemplary arrangement ofintermittent securement regions in the elastic composite of the presentinvention.

FIG. 15 is a plan view illustrating still another exemplary arrangementof an intermittent securement region in the elastic composite of thepresent invention.

FIG. 16 is a graph of the relationship between tensile strength of theelastic composite and the process temperatures at which the elasticcomposite is heat-compressed.

FIG. 17 is a perspective view illustrating an absorbent article whichincorporates the elastic composite of FIG. 13 as its side panel.

FIG. 18 is a graph showing S-S curves of the elastic composite asprepared in Example 1, the elastic sheet and the non-woven fabric asused in preparing the elastic composite of Example 1, respectively, whenthey are stretched in the CD.

FIGS. 19A, 19B and 19C are explanatory plan views illustrating surfacestructures after the second-stage treatment of Example 3, after thethird-stage treatment and after the fourth-stage treatment,respectively.

FIG. 20 is a graph showing results of a three-cycle test which repeatsthe 150% stretch and release of only the readily-stretchable portion ofthe elastic composite as prepared in Example 3.

FIG. 21 is a graph showing results of a three-cycle test which repeatsthe 150% stretch and release of only the hardly-stretchable portion ofthe elastic composite as prepared in Example 3.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

First, an explanation of stretch-activation is in order. FIGS. 1 and 2show typical S-S strain-stress) curves of elastic composites inaccordance with the present invention. Initial stretch of the elasticcomposite causes the elastic sheet and the non-woven fabric toexperience structural changes concurrently. The elastic compositeinitially shows a relatively high stress. Once the elastic composite isinitially stretched, the non-woven fabric has already elongated andexhibits less resistance to a second stretch. The elastic compositesubsequently exhibits the elastic characteristics of the elastic sheetat a second stretch, and similarly at a third stretch and stretchesthereafter. The appearance of such a phenomenon will be referred to asstretch-activation in this specification.

Another important feature of the stretch-activation is that the elasticcomposite exhibits its elasticity within ranges depending uponstretching rates, as illustrated in FIGS. 3 through 7. FIGS. 3-7,respectively, show S-S curves for an elastic composite similar to thatdepicted in FIG. 1, but with the maximum strain depicted being 50% (FIG.3); 75% (FIG. 4); 100% (FIG. 5); 125% (FIG. 6) and 150% (FIG. 7).Accordingly, when the elastic composite is applied to a user's body, itelastically stretches and contracts within a range corresponding tomovements of the user's body so that a flexible and efficient, fittingstructure can be provided.

The stretch-activation, in some cases, might occur automatically whenthe elastic composite attached to a final product is stretched uponwearing. However, it may be desirable that such stretch-activation bedone either prior to or during the production of a product using thecomposite. For instance, in an absorbent product using the elasticcomposite for a waist gather, the following two cases can be considered:(1) a previously stretch-activated elastic composite is used; or (2)stretch-activation of the elastic composite is done during theproduction process. In the former case, the material is bulky. In thelatter case, bulkiness will be less of a problem. During the productionof a product using the elastic composite which has not been previouslystretch-activated, a roll having deep corrugations or grooves in itsperipheral surface may be used in the production line for achievingpartial stretch in the elastic composite. In such a case, carefulattention is required to prevent damage to the surfaces of the non-wovenfabric and elastic sheet.

Such a stretch-activated elastic composite preferably shows low stressand a rapid increase in resistance as it exceeds a certain range ofstretching rate so that it stops stretching before it breaks. In otherwords, such composite shows low resistance to stretching in theactivated range but at the upper stretching limit it shows a rapidincrease in resistance to stretching.

It is further important that the elastic composite maintains its elasticcharacteristics even after being stretched and released repeatedly. Theimportant and basic characteristic of the elastic composite accordinglyresides in its low residual strain.

The characteristics of a preferred embodiment of the elastic compositeof the invention will now be described.

The following results of measurements for physical characteristics weredone according to methods commonly used in this field of industry andbased on the JIS (Japanese Industrial Standards) standards. Major pointsof the measurements are given below:

(1) Samples to be tested

Width: 5 cm

Length: 15 cm

(2) Measurement condition for S-S curves

Chuck distance: 10 cm

Loading speed: 20 cm/min.

(3) Cycle tests

Loading and unloading cycles are repeated three times at 150% stretchand hysteresis curves are obtained. Stress values are read at 30% and100% from the final returning point of the hysteresis curves. Betweenthe cycles, an ease time in which all loading is released, is given asshown below:

1^(st) Measurement—first 5 minute ease time—2^(nd) Measurement—second 5minute ease time—3^(rd) Measurement—third 5 minute ease time. Thehysteresis curves as shown in FIGS. 1 and 2 correspond to this cycle.Line A below shows the first loading cycle. Line A′ shows the recoveryduring the first ease time. Line B shows the second loading cycle. LineB′ shows the recovery during the second ease time. Line C shows thethird loading cycle. Line C′ shows the recovery during the third easetime.

An elastic composite 5 cm wide is sampled to measure an S-S curve duringits first cycle of stretch and release, showing the following desirablecharacteristics:

(1) Stress at 30% stretch

This shows the initial stress against stretch, which corresponds to thefirst expansion upon using. A 30% stretch is selected as an indicator,showing the initial stretch modulus, since it is commonly used in thefiber industry. This value should be selected carefully because toolarge an initial stress will create too tight a feeling. It has beenfound through experience, a desirable value is not more than 1,000 g,preferably 800 g and more preferably 600 g.

(2) Stress at 100% stretch

This is the stress necessary for stretch-activation, but may vary withusage or with the maximum degree of stretch upon using. In general, theelastic composite of the present invention displays its characteristicsat a highly stretched condition and will usually be used over 100%stretch, so that a stress at 100% stretch is selected for an evaluationpoint.

The elastic composite of this invention should have 400 g or more stressat 100% stretch, preferably 600 g, and more preferably 800 g stretch,thereby achieving desirable stretch-activation.

(3) Stress at a breaking point

A sufficient stress is usually 400 g or more. However, accidentalbreaking is less common when the stress is higher than 600 g, becauseone can more easily feel the resistance as the composite approaches thelimit of stretch.

Such an elastic composite will have a very low measured stress valueafter stretch-activation. For example, after being stretch-activated at150% stretch, the value when the composite is stretched less than 150%will be significantly decreased. Such decrease in stress is desirable inview of the objectives of the usage of the composite of the presentinvention.

Desirable S-S properties of an elastic composite of the presentinvention at 150% stretch are as follows:

(1) Stress at 30% stretch

The stress should be less than 500 g, preferably less than 400 g, andmore preferably less than 300 g following stretch-activation. Byselecting such stress levels, potentially uncomfortably high compressionon the body can be avoided when the elastic composite is used, forexample, in products for infants.

(2) Stress at 100% stretch

After stretch-activation, the stress at 100% stretch will becomesignificantly lower, while providing a suitable stretch resistance toprovide a secure fit to the wearer. The minimum stress is higher than100 g, preferably higher than 200 g.

A second S-S curve measurement shows the following characteristics:

(1) Stress at 30% stretch

Considering its conformability to a user, the stress is preferably lessthan 500 g, and more preferably less than 400 g.

(2) Stress at 100% stretch

The stress decreases by over 100 g, compared to the first measurement.

It is further important that the elastic composite exhibits a highelastic recovery rate, and accordingly a low residual strain. Inevaluating its performance in elastic recovery, the elastic recoveryrate generally is measured after three repeated cycles of stretching150% and then releasing the composite. The elastic recovery ratio isdetermined by comparing the returning point (P1), such as shown in FIG.2, against the staring point (P0) against the whole elastic ratio. Forexample, assuming point P1 is at 30% for an elastic ratio of 100%, therecovery ratio is calculated by the following formula:

Recovery Ratio=100−P1−P0/150×100=100−(30/150×100)=80(%)

The desirable elastic recovery rate is higher than 60%, and preferablyhigher than 70%. Constituent elements of the elastic composite havingsuch elastic recovery will now be explained.

The elastic sheet to be used preferably is selected from materialshaving stretchability of higher than 20% and elastic recovery of higherthan 60%. Materials having such characteristics include foams such as ofurethanes or rubber latexes; synthetic rubber films such as of isoprenesor butadienes; styrene-type elastomer films such as of SIS (styleneisoprene stylene), SEBS (stylene ethylene butadiene stylene), and SEPS(stylene ethylene propylene stylene); polyolefin elastomer films such asof EVA (ethyl vinyl acetate), EMA (ethyl methyl acrylate), and EPDM(ethylene propylene diene terpolymer); and meltblown elastomernon-wovens such as polyurethane, SIS (stylene isopreren stylene) andSEBS. The elastic sheet more preferably comprises a film, net-likeformation, or meltblown non-woven, formed of heat-sealable styrene-typeelastomers such as SIS or SEBS, or blends thereof.

The constituent element of the elastic composite of the presentinvention, the non-woven, will now be explained.

The most suitable presently known non-woven fabric for use in thepresent invention is a hydro-entangled or spunlaced non-woven fabric,preferably having high elongatability in the machine direction (MD) orin the cross-direction (CD). The non-woven fabric having highCD-elongatability can be obtained by hydro-entangling a longitudinallyoriented, parallel carded web which has a high MD/CD ratio, i.e., thefibers extend predominantly in the machine direction. The non-wovenfabric having high elongatability in the MD can be obtained byhydro-entangling a randomly oriented fibrous web comprising highlyshrinkable fibers, overfeeding the entangled web in the MD and dryingbefore it is treated to shrink.

Such MD-elongatability or CD-elongatability is preferably higher than100%, and more preferably higher than 200%.

The elongatability of the non-woven fabric allows the non-woven fabricto follow the action of the elastic sheet when they are combined witheach other.

The non-woven fabric has another important characteristic as well as itselongatability.

As the elongation of the non-woven fabric exceeds a certain extent, thenon-woven fabric starts showing resistance to further elongation.

For comparison, FIG. 8 shows exemplary CD and MD Stress-Strain (S-S)curves of three different non-woven fabrics designated Nos. 1, 3 and 5which are respectively prepared by hydro-entangling normal parallel websby conventional means. As apparent from FIG. 8, these non-woven fabricsare highly elongatable in the CD. No resistance appears when each of thenon-woven fabrics exceeds its elastic limit before it finally breaks.

In contrast, a spunlaced non-woven fabric (which also may be known as a“hydro-entangled non-woven” or a “water jet entangled non-woven”) showsrapid increase in stress at about 200% stretch as illustrated in FIG. 9.With the stress maintained, the non-woven fabric continues to elongateuntil it breaks at a breaking point (about 260% stretch). Thissecond-phase increase in stress at about 200% stress acts to resistbreaking before the non-woven fabric finally breaks. It is desirable toselect physical properties of the non-woven fabric so that thesecond-phase increase in stress takes place preferably at higher than150% stretch, and more preferably at higher than 200% stretch.

In order for the non-woven fabric to exhibit such characteristics, thefibrous web construction and the condition for hydro-entanglementthereof need to be selectively combined.

For example, the following non-woven fabric meets such requirements.

(1) Web construction

Relatively short staple fibers of 25-45 mm long are mixed withrelatively long staple fibers of 45-60 mm long to prepare raw staplefibers.

Fibers are further mixed therein which are capable of shrinking tocrimp.

(2) Selection of condition for hydro-entanglement

Hydro-jets from fine nozzles integrally entangle fibers in the web overits whole area, and thereafter intensely hydro-entangle the web attransverse intervals. For example, three parallel rows of the nozzlesare disposed to hydro-entangle the fibers in three stages:

First stage: nozzle diameter: 0.15 mm φ nozzle pitch: 0.5 mm waterpressure: 30 kg/cm² Second stage: nozzle diameter: 0.15 mm φ nozzlepitch: 0.5 mm water pressure: 50 kg/cm² Third stage: nozzle diameter:0.20 mm φ nozzle pitch: 1.0 mm water pressure: 60 kg/cm²

A spun-laced non-woven fabric having a striped pattern is obtained underthe above conditions.

The elastic composite of the present invention comprises an elongatablenon-woven fabric bonded to a top surface or to the top and bottomsurfaces of the elastic sheet. Although the bonding method is notspecifically limited, different bonding methods may cause the resultantelastic composite to have different characteristics. Regardless of theselected bonding method, the following factors become important:

(1) The non-woven fabric is bonded to the elastic sheet so that thereadily elongatable direction of the non-woven fabric is brought intoagreement with the readily stretchable direction of the elastic sheet.

(2) The bonding is made to form securement regions in a selected patternso that it does not disturb effective elongation of the non-woven fabricand effective stretching of the elastic sheet. To this end, it isdesirable that the securement regions are arranged to define as small innumber and area as possible in the readily elongatable direction. Suchbonding can be easily made by distributing securement regions,preferably in the range of 90° (+10°), with respect to the readilyelongatable direction of the non-woven fabric.

(3) When non-woven fabric is placed on opposite surfaces of the elasticsheet, the placement of the securement regions respectively between theone non-woven fabric and the elastic sheet and between the othernon-woven fabric and the elastic sheet greatly affect the elasticcharacteristics of the formed elastic composite. In an elastic compositehaving an elastic sheet positioned between two non-woven fabrics, theelastic sheet may comprise one sheet of an elastic film of 50 μm thickor two sheets of an elastic film of 25 μm, supposing that the desirablethickness of the elastic sheet is selected to be 50 μm. However, itshould be recognized that 50 μm is used as an example and otherthicknesses may be used as well. FIGS. 10A, 10B and 10C illustrate threetypical alternative embodiments for combining the elastic sheet and thenon-woven fabric.

In FIG. 10A two elastic sheets 11, 12 each having a thickness of 25 μmare bonded at securement regions 3 to two non-woven fabric sheets 21,22, respectively to form two elastic composites 20A, 20B which arebonded to each other by hot pressing as in region 4.

In FIG. 10B two elastic sheets 11, 12 each having a thickness of 25 μmare placed and bonded between two non-woven fabrics 21, 22 throughsecurement regions 3 such as by hot pressing.

In FIG. 10C an elastic sheet 13 of 50 μm thick is positioned between twonon-woven fabric sheets 21, 22 and bonded thereto at securement regions3.

An S-S curve is measured for each construction illustrated in FIGS. 10A,10B and 10C. Each construction is stretched by 100% and subsequentlyreleased to compare its length with its initial length prior tostretching. Better elastic recoveries are observed in 10B than 10C, andin 10A than 10B, respectively.

In FIG. 10A, the securement regions 3 of the elastic sheet 11 and thenon-woven fabric 21 are staggered from the securement regions 3 of theelastic sheet 12 and the non-woven fabric 22. The securement regions 3upon which tensile stress is concentrated are arranged in differentlocations between the top and the bottom of the elastic composite sothat the formed elastic composite has a relatively high tensilestrength.

The industrial process for combining two sheets of a relatively thinone-sided composite to form a two-sided composite also improvesproduction efficiency. Especially when polystyrene-type elastomer filmssuch as SIS or SEBS are used for the elastic sheet, the stable two-sidedcomposite can be readily manufactured by simply placing the filmsurfaces of the two composites onto each other and hot-pressing themsince those films are highly heat-bondable. This greatly improvesproductivity and cost-savings.

Both elastic composites have the non-woven fabric securely placed uponone surface thereof. As illustrated in FIGS. 10A, 10B and 10C,securement regions 3 respectively extend in a band-like mannertransversely to, and preferably at angles of 90° (+10°), with respect tothe readily elongatable and stretchable direction of the non-wovenfabric and the elastic sheet.

The band-like securement regions may secure the non-woven fabric and theelastic sheet entirely over a specified area. Alternatively, theband-like securement regions may comprise a plurality of securementsegments arranged in a row toward a selected direction, such as aplurality of dots or line segments distributed in a desirable patternedmanner over the specified area.

FIG. 11A, 11B and 11C illustrate typical examples of the patternedsecurement segments arranged at intervals. In FIG. 11A, each of thesecurement segments 31 comprises a relatively short line segment. Thesecurement segments 31 are arranged at suitable intervals in rowsextending in a direction substantially transversely to the readilystretchable direction of the elastic composite to define a plurality ofrows 30 of securement segments extending in parallel to each other. InFIG. 11B, each securement segment 31 comprises a line segment andextends substantially transversely to a longitudinal direction of therow 30 of securement segments. In FIG. 11C, each securement segment 31is substantially Y-shaped, although it may have any selected shape aswell as the illustrated shapes.

The elastic composite sacrifices the inherent expansibilities of thesematerials in the securement regions which secure the non-woven fabric tothe elastic sheet so that it is rendered substantially inelastic in thesecurement regions. Accordingly, when the provisions of the rows 30 ofsecurement segments are made to extend substantially transversely to thereadily-stretchable direction as illustrated in FIGS. 11A, 11B, and 11C,such provisions greatly reduce the stretchability of the elasticcomposite in the direction parallel to the readily stretchable directioneven if the materials themselves are highly stretchable in suchdirection. Substantially, the elastic composite constructions asillustrated in FIG. 11 expand to a very slight extent in thelongitudinal direction of the rows 30 of securement segments.

The elastic composite exhibits greatly reduced stretchability in thesecurement regions even when the non-woven fabric and the elastic sheetare combined by hydro-entanglement to provide such securement regions.In contrast to the elastic composite as described in Japanese UtilityModel No. 3-39509, the elastic composite of the present inventionstretches very slightly in the regions where the non-woven fabric andthe elastic sheet are tightly hydro-entangled.

However, the elastic composite expands freely in the readily expandabledirection transversely to the rows 30 of securement segments until itreaches the elastic limit of the non-woven fabric. The elastic compositereturns to its initial length when the tension is released prior toreaching the upper limit. On the other hand, as the elastic composite isfurther stretched beyond the elastic limit, the non-woven fabricundergoes permanent elongation and never returns to its initial lengtheven after release of the tension. The elastic sheet sustains itselasticity because its elastic limit is much higher than that of thenon-woven fabric, and returns to its initial length after release of thetension. When the elastic composite returns to its initial length uponrelease, the non-woven fabric becomes pouched between the neighboringrows of securement segments.

Once the non-woven fabric undergoes permanent elongation, a smallerforce is thereafter required to stretch the elastic composite in thereadily stretchable direction than is required when it is initiallystretched beyond the elastic limit of the non-woven fabric. Thisphenomenon typically defines the stretch-activation as mentioned above.

As will be appreciated from the above description, the elastic compositeis more resistant to stretching in the direction that the securementregions extend than in the readily stretchable direction thereof Thesecurement segments permit the elastic composite to have itsstretchability generally tailored in a desirable and specifieddirection.

FIG. 12A shows a substantially rectangular elastic composite comprisingan elastic sheet and a non-woven fabric which are highly stretchable inboth the x and y directions, respectively. As illustrated in FIG. 12B,the elastic composite includes peripheral areas B, C of suitable widthsrespectively extending along its four linear edges to enclose a centralarea A. Each of the peripheral areas has linear securement regions 3which extend transversely to and inwardly from their respective linearperiphery. The illustrated elastic composite is stretchable in anydirection in the central area A, only in the x direction in theperipheral areas B, and only in the y direction in the peripheral areasC.

FIG. 12C shows an elastic composite which includes end areas B extendingalong opposite ends of the elastic composite and an area D extending inthe y direction along the composite centerline. Those areas haverespective linear securement regions 3 extending in the y direction. Theelastic composite further includes end areas E extending along oppositeends thereof. The end areas E have linear securement regions 3 whichextend at an angle of about 45° from the respective linear peripheries.Accordingly, the elastic composite is highly stretchable in thex-direction in its areas B and D, and is stretchable in a slantingdirection in the end areas E, normal to securement regions 3 in areas E.

Because the elastic composites of FIG. 12B or FIG. 12C have selectedareas stretchable only in the respectively specified directions, theycan be advantageously used for an elastic topsheet or backsheet of adisposable diaper. In such an event, the end areas B, the end areas C, Eand the central area A may serve as waist elastics, leg elastics andexpansive elastics for elastically contracting and stretching over anarea of the diaper. This enables one to selectively design desirableproducts which are capable of following any configuration.

FIG. 13 shows still another elastic composite embodiment of the presentinvention. An plastic composite 100 is stretchable in only onedirection. The elastic composite is highly stretchable in its firstcentral area 110 and is less stretchable or only slightly stretchable inits second opposite end areas 111. The elastic composite with suchcharacteristics can be obtained by applying further bonding treatmentsuch as partially heat-compression treatment to the elastic composite asprepared in the above-mentioned manner.

In FIG. 14, an elastic composite has three slightly-stretchableband-like areas 111 disposed at regular intervals.

An elastic composite of FIG. 15 has highly-stretchable areas 110 onopposite sides of a slightly-stretchable band-like area 111. In theseillustrated embodiments, the elastic composites comprise an elasticsheet and a non-woven fabric which are both formed of readilyheat-fusible materials.

Examples of non-woven fabrics suitable for such requirement includeconjugate fibers consisting of a polyester core covered withpolyethylene sheath, which is combined with a film of S.E.B.S.(styrene-ethylene-butadiene-styrene block polymer) as an elastic sheet.This material may be easily ultrasonically or heat sealed, and can beused in a high speed production process.

The elastic composites having a highly-stretchable area 110 and aslightly stretchable area 111 is illustrated in FIGS. 13 and 15 can beobtained by applying heat of a suitable temperature range to the area111.

FIG. 16 is a graph showing the results measured with regard to arelationship between tensile strength of an elastic composite andtemperatures at which the elastic composite is heat-compressed. Theelastic composite is prepared by placing an elastic sheet formed ofSIS-type film upon a hydro-entangled non-woven fabric comprising PET(polyester) fibers and thereafter partially heat-compressing them forintegration. The characteristics of the elastic composite illustrated inFIG. 16 are obtained by further applying heat and compression to theintegrated elastic composite.

In the graph, T1 indicates the temperature at which SIS present in theelastic sheet starts to melt and T2 the temperature at which PET presentin the non-woven fabric starts to melt, respectively. As can be seenfrom FIG. 16, heat-compression below T1 is not sufficient to integratethe elastic sheet and the non-woven fabric so that the elastic compositeexhibits low tensile strength while sustaining good elastic recovery.When the heat-compression is applied to the elastic composite at atemperature ranging from T1 to T2, at least part of the elastic sheetmelts and is fused to the non-woven fabric so that the elastic compositeexhibits greatly enhanced tensile strength while recovery is lost.Heat-compression above T2 causes the elastic sheet and the non-wovenfabric to be bonded so that the elastic composite exhibits reducedstretchability in all directions.

Referring again to FIGS. 13 and 15, the elastic composites of thosecharacteristics also can be obtained by utilizing differentheat-compressive conditions between area 110 and the area 111 whenheat-bonding the elastic sheet and the non-woven fabric which are placedupon each other so as to be stretchable in the same direction.Specifically, the elastic sheet and the non-woven fabric are partiallyheat-compressed in the area 110 at a temperature ranging between T1 andT2 and are entirely heat compressed in the area 111 at a temperatureabove T1 to render the areas 110 highly-stretchable and the area 111slightly stretchable. Accordingly, the desirable stretchability can begiven to the elastic composite in such a manner. Because thestretchability of the highly-stretchable area 110 is restrained byslightly-stretchable area 111, the elastic composite ischaracteristically highly stretchable in a specified direction and isslightly stretchable in other directions.

Such elastic composites have highly stretchable and slightly-stretchableareas disposed in a mixed and patterned manner can be applied to varioususes. For example, the elastic composite having the slightly-stretchableareas 111 disposed on opposite sides of the highly-stretchable area 110such as illustrated in FIG. 13 can be applied to tapeless (pant-type)absorbent articles.

FIG. 17 illustrates an absorbent article, such as a tapeless diaper, oftraining pant, having a main body 121 comprising an absorbent bodyinterposed between a liquid permeable topsheet and a liquid impermeablebacksheet. The main body is bent along its center line to define asubstantially U-shaped configuration. An elastic composite 100 connectsopposite side edges of the U-shaped main body to define a leg hole 122.The elastic composite 100 has the slightly-stretchable, opposite endareas 111 connected to the main body 121 and the highly-stretchablecentral area 110 rendered free, so that the highly-stretchablecharacteristics of the area 110 are not disturbed. The elastic composite100 is connected at its opposite ends to the main body 121 to serve as aside panel of the diaper or training pants.

Examples of the present invention will now be described.

EXAMPLE 1

Manufacture of an Elongatable Non-woven Fabric

50 parts of polyester fibers (1/5 denier×35 mm) are mixed with 50 partsof polyester fibers (2 denier×51 mm). The mixture is introduced into aroller card to prepare a parallel carded web having a basis weight of 25g/m².

The web has an orientation ratio MD/CD of 7. In other words, thestrength of the web in the machine direction (MD) is seven times itsstrength in the cross direction (CD). The web is introduced over aporous suction cylinder provided with a dewatering zone while subjectedto water-saturation, degassing and dewatering. The web is then passed ata running speed of 30 S m/min under three banks of water nozzles forwater-entanglement.

First nozzle: 0.12 mm diameter × 0.4 mm pitch (distance between adjacentnozzles in a bank) water pressure 30 kg/cm² Second nozzle: 0.12 mmdiameter × 0.4 mm pitch water pressure 50 kg/cm² Third nozzle: 0.20 mmdiameter × 1.5 mm pitch water pressure 60 kg/cm²

The entangled web as described above is dried and subsequently issubjected to heat treatment so that a web-form non-woven fabric having abasis weight of 30 g/m² is obtained.

An S-S curve of this non-woven fabric when stretched in CD is indicatedat A in FIG. 18.

Preparation of an Elastic Sheet

A blend resin comprising EMA/EPDM (ethyl methyl acrylate/ethylenepropylene diene terpolymer) polyolefin elastomer is extruded to form afilm of 25 μm thick. An S-S curve of this elastic sheet when stretchedin CD is indicated at B in FIG. 18.

One-sided Composite

The elastic sheet and the non-woven fabric as prepared above aresuperposed and laid over a 60-mesh PET net with the elastic sheet sidefacing toward the PET net. A heated roller having patterned annulargrooves thereon is applied to the non-woven side while heated to 130° C.A flat or non-grooved roller is disposed beneath the PET net. The heatedroller is pressed against the elastic sheet and fabric so that they arecompressed against the flat roller at a line pressure of 10 kg/cm toform an elastic composite.

An S-S curve of the elastic composite thus produced when stretched inthe CD is indicated at C in FIG. 18.

A three-cycle test which repeats the 150% stretch and release of theelastic composite provides results as shown FIG. 1. The measuredrecovery rate is 75%.

Two-sided Composite

Two sheets of the above elastic composite are placed upon each other sothat their film sides face toward each other. A non-grooved surfaceheated roller heated up to 80° C. applies pressure to the sheets at aline pressure of 20 kg/cm and at a speed of 10 m/min so that a stablebonding condition is provided between the facing film sides of the twosheets. The securement regions in top and bottom sides are staggeredfrom each other. An S-S curve of the resulting elastic composite isindicated by D in FIG. 18.

A three-cycle test which repeats the 150% stretch and release of thiselastic composite provides results as shown in FIG. 2. The measuredrecovery rate is 75%.

EXAMPLE 2

One-sided Composite Comprising a SEBS-type Film and a Non-woven Fabric

A composition primarily comprising a mixture of 75 parts SEBS and 25parts EVA is extruded to prepare an elastic film of 25 μthick.Characteristically, this film can be easily bonded onto itself bycompression at room temperature.

A slight amount (about 0.4 g/m²) of rubber-type hotmelt adhesive issprayed onto one surface of the film which then is bonded over itsentire surface to a non-woven fabric similar to the one prepared inExample 1.

Two-sided Composite

Two sheets of the above elastic composite having the non-woven fabricsecured on one side of the SEBS-type film are placed upon each other sothat their respective film sides face toward each other. These twosheets are passed between a pair of non-grooved rolls at a temperatureof about 40° C. and under a line of pressure of 20 kg/cm² to provide atwo-sided composite which has the non-woven fabrics on its oppositesides and films stably secured to each other.

The one-sided and two-sided composites thus constructed show elasticrecoveries similar to those of Example 1.

EXAMPLE 3

70 parts of polypropylene fibers (2 denier×30 mm) are mixed with 30parts of polyester fibers (2 denier×57 mm). The mixture is introducedinto a roller card to prepare a parallel carded web having a basisweight of 20 g/m². The web has a MD/CD ratio of 8.0.

The web is introduced over a net conveyor where it is placed upon amelt-blown non-woven fabric (manufactured by KURARAY Co., Ltd.)primarily constituted of SIS and having a basis weight of 40 g/m². Thecombined web and non-woven fabric are then introduced over a netprovided with nozzles and a dewatering zone where they are subjected toa multi-stage hydro-entanglement treatment as detailed in the followingTable 1.

TABLE 1 Surface appearance of the obtained elastic Stage Nozzle spec.Pressure composite First stage 0.12 mmφ × 0.6 mm  30 kg/cm² —(provisional stage) Second stage 0.12 mmφ × 0.6 mm  50 kg/cm² Figure 19A(provisional stage) Third stage 0.20 mmφ × 4.0 mm 100 kg/cm² Figure 19B(partial entanglement) Fourth stage 0.15 mmφ × 0.6 mm  80 kg/cm² Figure19C (partially inelasticizing treatment)

The surface structures of the composites obtained at various stages areshown in FIGS. 19A, 19B and 19C. The entangled elastic composite afterthe final stage has band-like readily-stretchable portions 131 andhardly-stretchable portions 132. A three-cycle test which repeats the150% stretch and release of only the readily-stretchable portion 131 ofthe elastic composite provides results as shown in FIG. 20. The measuredrecovery rate is 70%. On the other hand, the hardly stretchable portion132 hardly contracts elastically and provides a S-S curve as shown inFIG. 21. Its breaking point is shown to be 1.2 kg/50 mm.

As described above, the elastic composite in accordance with the presentinvention comprises a non-woven fabric which is potentially elongatableby higher than 100% in a specific direction, and an elasticallyrecoverable elastic sheet. The non-woven fabric in its unelongated stateis bonded to at least one surface of the unstretched elastic sheetthrough securement points to form the elastic composite which hasrecovery rate of higher than 60% after experiencing the three-repeatedcycles of 150% stretch and release. Therefore, the elastic composite ofthe present invention provides excellent performance in elastic recoveryand has a soft touch to the human skin. In particular, the elasticcomposite of the present invention can be advantageously utilized inelasticizing an article which is brought into direct contact with thehuman skin, such as a sleeve of a medical gown, or a waist or crotchportion of a sanitary article.

Although various embodiments of the invention have been describedherein, it will be recognized that variations and modifications arepossible without departing from the spirit of the invention as set outin the claims.

What is claimed is:
 1. A stretch activated elastic composite comprising:a first non-woven fabric sheet adapted to be elongated by more than 100%in one direction; and a first elastically recoverable, elastic sheet;said first elastic sheet in its unstretched state being bonded atsecurement regions to one surface of said first non-woven fabric sheetin its unelongated state; said elastic composite before stressactivation having, per unit width of 5 cm, when stretched in said onedirection (1) a stress of lower than 1000 g at 30% stretch, (2) a stressof higher than 400 g at 100% stretch, (3) a breaking point of higherthan 400 g, and (4) an elastic limit of higher than 200%, said elasticcomposite after stress activation by being stretched to an elongation ofless than 200% having, per unit width of 5 cm, (1) a stress of lowerthan 500 g at 30% stretch and (2) a stress of higher than 100 g at 100%stretch, and said elastic composite after three repeated cycles of 150%stretching and relaxing having an elastic recovery rate of higher than60% when measured based on JIS standards.
 2. The elastic composite ofclaim 1, further comprising a second non-woven fabric sheet and whereinsaid first non-woven fabric sheet and second non-woven fabric sheet arebonded to opposite surfaces of said elastic sheet.
 3. The elasticcomposite of claim 2, further comprising a second elastic sheet andwherein said first and second elastic sheets each have a first surfaceand an opposed second surface, said first non-woven fabric sheet bondedat said securement regions to the first surface of the first elasticsheet, said second non-woven fabric sheet bonded at second securementregions to the first surface of the second elastic sheet, and the secondsurfaces of said elastic sheets are bonded to each other.
 4. The elasticcomposite of claim 3 wherein: said securement regions between said firstnon-woven fabric sheet and said first elastic sheet are offset from thesecond securement regions between said second non-woven fabric sheet andsaid second elastic sheet.
 5. The elastic composite of claim 1 whereinsaid securement regions which bond said first elastic sheet and saidnon-woven fabric extends in an elongate band in a direction extendingtransversely of said one direction.
 6. The elastic composite of claim 1wherein said securement regions which bond said first elastic sheet andsaid first non-woven fabric are arranged in rows which extend in adirection transversely of said one direction.
 7. The elastic compositeof claim 1 wherein said first non-woven fabric comprises a fabricproduced by water-entanglement and having a two-phase expandability atdifferent stress levels.
 8. The elastic composite of claim 7, whereinsaid first non-woven fabric comprises a fabric whose elongation at asecond phase takes place at an elongation rate of higher than 150%. 9.The elastic composite of claim 1 wherein said first elastic sheetcomprises heat-fusible material.
 10. The elastic composite of claim 9,wherein said first elastic sheet and said first non-woven fabric are, ina specified area of the elastic composite, bonded to each other by heatcompression above a temperature at which the first elastic sheet startsto melt but below a temperature at which the first non-woven fabricstarts to melt to form a slightly-stretchable portion which is moreresistant to stretching than the remaining portions.
 11. The elasticcomposite of claim 10, wherein said slightly-stretchable portion isprovided in a band-like manner.
 12. The elastic composite of claim 9,wherein said first non-woven fabric consists of conjugated fibers whichare easily fusible by heat.
 13. A stretch-activated elastic compositecomprising: a first non-woven fabric having a potential elongatabilityof higher than 100% in one direction; and a first elasticallyrecoverable, elastic sheet; said first elastic sheet in its unstretchedstate being bonded to at least one surface of said first non-wovenfabric in its unelongated state at securement points, said first elasticcomposite before stress activation having, per unit width of 5 cm, (1) astress of lower than 800 g at 30% stretch, (2) a stress of higher than600 g at 100% stretch, (3) a breaking point of higher than 400 g, and(4) an elastic limit of higher than 200%, said first elastic compositeafter stress activation by being stretched at a rate of lower than 200%having, per unit width of 5 cm, (1) a stress of lower than 300 g at 30%stretch and (2) a stress of higher than 200 g at 100% stretch, and saidfirst elastic composite after three repeated cycles of 150% stretchingand relaxing having an elastic recovery rate of higher than 60% whenmeasured based on JIS standards.
 14. A stretch-activated elasticcomposite comprising: a non-woven fabric sheet adapted to be elongatedby more than 100% in one direction; and an elastic sheet having anelastic recovery rate of higher than 60% and an elastic limit of higherthan 200%; said elastic sheet in its unstretched state being bonded atsecurement regions to one surface of said non-woven fabric sheet in itsunelongated state; said elastic composite before stress activationhaving, per unit width of 5 cm, when stretched in said one direction (1)a stress of lower than 1000 g at 30% stretch, (2) a stress of higherthan 400 g at 100% stretch, (3) a breaking point of higher than 400 g,and (4) an elastic limit of higher than 200%, said elastic compositeafter stress activation by being stretched to an elongation of less than200% having, per unit width of 5 cm, (1) a stress of lower than 500 g at30% stretch and (2) a stress of higher than 100 g at 100% stretch, andsaid elastic composite after three repeated cycles of 150% stretchingand relaxing having an elastic recovery rate of higher than 60% whenmeasured based on JIS standards.